The interaction of endogenous opiate peptides with obesity will be examined. Beta-endorphin concentrations and forms in discrete brain nuclei, anterior and neurointermediate pituitary lobes and plasma will be determined in genetically and diet-induced obese vs food restricted and lean animals of various ages to clarify whether elevated concentrations arise from or contribute to the onset of obesity. The studies will utilize radioimmunoassay, gel column chromatography, isoelectric focusing and gel electrophoresis to assess concentrations and forms of immunoreactive Beta-endorphin. Possible alterations in pain sensitivity will be assessed in chronically obese vs lean animals. Acute changes in beta-endorphin concentration and form which may occur in short term food deprivation and refeeding will be examined, as well as the effect of administration of beta-endorphin, naloxone and certain neurotransmitter agonists and antagonists on food intake. Studies will seek to determine whether other endocrine abnormalities common to obesity such as hyperinsulinemia and certain reproductive deficiencies are related to elevations of beta-endorphin.